Many times, a vehicle's battery is unable to provide enough cranking power to start the engine. This is often true during particularly inclement weather, or in the case of diesel power vehicles which are not used frequently. Thus, it is often necessary to provide such vehicles with a "jump" or an extra supply of power, by some external source.
Typically, this is done by connecting jumper cables from a fully powered vehicle to the disabled vehicle. For example, the operator of a car with a 12 volt battery would start its engine, and jumper cables would be connected from the terminals of the battery of the running vehicle to the terminals of the battery of the disabled vehicle. The voltage of the electrical system of the running vehicle is typically between 14-16 volts, the voltage above 12 volts being created by the vehicle's alternator. When an attempt is made to start the disabled vehicle, current is drawn from the running vehicle. When the amount of the current draw exceeds the output amperage of the alternator, the voltage will have dropped to that of the running vehicle's battery. The typical alternator can provide only about 60 amps. Current requirements beyond that can only be supplied from the battery. There again, as current is drawn from the battery, the voltage will drop accordingly. It is hoped that the power of the running vehicle is sufficient to start the disabled vehicle. However, if the current draw is too high, then the voltage of the running vehicle will drop to a level too low to spark the plugs. In such a case, no amount of cranking will start the engine. Thus, it may be necessary to supply the charging vehicle with more power than a normal 12 volt battery can supply.
The amperage necessary to start a disabled vehicle increases as the temperature of the engine decreases. In low temperatures, there is more internal friction due to the fit of the components and the viscosity of the oil than when the temperature is warm. This results in a need for higher torque to rotate the crank shaft during starting Additionally, large vehicles with large engines usually require more torque during starting. In certain cases, it may be necessary for extended cranking of the engine during starting because the engine's problem is not in the rotating of the crank shaft, but in other areas, such as a flooded carburetor. Extended cranking can quickly drain the battery of even an operatable vehicle.
To provide the necessary amperage for these conditions, a service vehicle may include a generator powered by a separate engine. To use such a system, the engine is started and the output of the generator is connected to the disabled vehicle. The generator is sized to provide as much as 1,200 cold cranking amps at a voltage in the range of 14 to 16 volts. Such a system is both expensive and noisy to operate, and takes up space in a service vehicle.
A typical prior art jump start system is disclosed in U.S. Pat. 3,105,910 to Chambers. In this patent, a service vehicle is equipped with a 12 volt service vehicle battery, and a 12 volt auxiliary battery. When servicing a disabled battery with a 6 volt battery, the service truck battery is connected in parallel to the dead battery. When servicing a 12 volt battery, the service truck battery and auxiliary battery are connected in series, and then connected to the disabled 12 volt battery in parallel. This arrangement will most certainly provide the dead battery with a sufficient charge to start the vehicle. However, connecting the dead battery to one with twice the voltage output is likely to damage the battery, as well as blowing dash bulbs and any computers on the disabled vehicle. A similar arrangement is disclosed in U.S. Pat. No. 3,343,057 to Smith.
The prior art also discloses systems which are used to provide an extra supply of power to a disabled vehicle. These systems are stored and used only on the disabled vehicle. U.S. Pat. No. 1,924,959 to Patterson shows a storage battery apparatus used in conjunction with a 6 volt vehicle battery. This apparatus was patented when typical automobile engines used a 6 volt battery. In this invention, an extra 2 volt cell is added to the normal 6 volt battery giving it a capability of 8 volts. This new battery would replace the existing 6 volt battery within the automobile. The 2 volt battery was normally connected in parallel to the remaining three 2 volt cells of the battery. If the car would not start under the power supplied by the 6 volt battery, the 2 volt battery could be connected in series to the 6 volt battery providing an 8 volt battery to supply power to the automobile.
U.S. Pat. No. 4,004,208 to Tamminen shows another on board vehicle starting aid. This system utilizes a pair of auxiliary batteries, each being 12 volts. However, these batteries are only able to provide a current on the order of 10 amperes. This system provides only a minimal amount of extra power to the dead battery, and which would be insufficient to start heavy duty or diesel equipment.
The limitations of the prior art listed are obvious. The Smith '057 and Chambers '910 devices both utilize a 24 volt source to start a 12 volt battery powered vehicle. Using this type of system is potentially very dangerous to the dead battery, as well as other parts of the vehicle. The Patterson '959 and Tamminen '208 devices are on board systems and provide only a small additional charge. These units would be ineffective if the battery was completely dead, or if the vehicle being charged had a diesel engine or was a heavy duty vehicle.